1. Field of the Invention
The present invention relates to a method of transmitting a video signal including a plurality of scanning lines, and more particularly to a method of transmitting a video signal in which additional information other than a video signal is transmitted using a vertical blanking interval (VBI) corresponding to an ineffective area of an image.
Specifically, the present invention relates to a video signal transmission method in which particular additional information such as copy management information or copyright protection information is transmitted using a particular scanning line in a VBI. More specifically, the present invention relates to a video signal transmission method in which a code is assigned to a particular scanning line in a VBI for transmission of additional information.
2. Description of the Related Art
In the art of information processing and information communication, it is known to insert additional information other than a content such as an image and a voice/sound into content data in such a manner that the inserted additional information does not cause impairment of the quality of the content.
An example of additional information embedded in a content is content copy management information or copyright protection information. In recent years, great advances have been made in the digital signal processing technology, the data storage technology, and the data transmission technology. As a result, recording/playback apparatuses and recording media with very small sizes have become available, and it has become possible to perform extremely high-quality data processing using an inexpensive apparatus. Accordingly, there is a great need for a technique of protecting copyright of contents.
In the case of a video content, additional information can be embedded in a non-image part such as a vertical blanking interval (VBI) of a video signal. Several techniques of embedding various kinds of additional information in a VBI of a video signal have been proposed, and some of them are practically used. Specific examples include techniques described in EIAJ-CPR1204 (video ID signal transmission method using a VBI), IEC (International Electrotechnical Commission)-61880, EDTV2, VPS, PDC, and XDS. In recent years, a technique of transmitting CGMS-A (Copy Generation Management System-Analog) describing copy management information by means of inserting it into a VBI has put to practical use. In particular, copyright protection and copyright management are important for content distributors, and thus insertion of copy management information has higher priority form them than other additional information.
Techniques of transmitting additional information by means of embedding it in an HDTV signal such as a 750P signal (noninterlaced 60-frame 750-line signal) or a 1125i signal (interlaced 60-frame 1125-line signal) are being discussed toward standardization independently in the USA and Japan.
In Japan, in preparation for starting BS digital broadcasting, specifications have been established under the leadership of EIAJ (Electronic Industries Association of Japan) and disclosed in a technical report CPR1204-2 (Video ID Signal Transmission Using a VBI). A recommendation of bit assignment associated with CGMS-A has been made by ARIB (Association of Radio Industries and Businesses).
In the USA, a similar activity to that in Japan is being performed by EIA (Electronic Industries Association). However, the standard proposed by EIA is different from that proposed in Japan. It is required that at least specifications associated with transmission of CGMS-A should be common between the USA and Japan to ensure protection of copyright of broadcasting contents in these two countries. To achieve the above requirement, the discussion is directed toward establishment of a common waveform and common assignment of CGMS-A. However, assignment associated with items other than CGMS-A will become different between the USA and Japan because of different requirements in these countries.
Even if common bit assignment associated with CGMS-A is established, a difference in assignment of the other bits may cause an erroneous operation when two devices one of which is based on the USA standard and the other on the Japanese standard are connected to each other.
The problems will be discussed in further detail below for the case of television broadcasting according to the current NTSC standard in which 525-line interlaced scanning is used.
In the NTSC standard, as is known, a period from 1st to 21st scanning lines and a period from 264th to 284th scanning lines of a video signal (more specifically, of a luminance signal) are respectively assigned to vertical blanking intervals (VBI). FIGS. 1 and 2 illustrate examples of bit assignment in the respective VBIs. As shown in FIGS. 1 and 2, the 20th scanning line and the 283rd scanning line are assigned to locations where CGMS-A is inserted. Basically, the same information is transmitted in the 20th and 283rd scanning lines.
FIG. 3 illustrates an example of a signal waveform transmitted in the 20th and 283rd lines. As can be seen from FIG. 3, each of these scanning lines includes an identification signal consisting of 20 bits following a reference bit.
In the Japanese standard, the first 2 bits of the 20-bit identification signal are assigned to WORD0, the following 4 bits to WORD1, the next 8 bits to WORD2, and the remaining 6 bits to CRCC (Cyclic Redundancy, Check Code, refer to FIG. 4). WORD0 is used to describe information about an aspect ratio, WORD1 is used to describe header information, and WORD2 is used to describe a body of data. According to the Japanese standard, when CGMS-A is described in WORD2, “0000” is described in the header or WORD1 to indicate that CGMS-A is described in WORD2.
According to the USA standard being under discussion, the first 6 bits of the 20-bit identification signal are assigned to a single word. However, to achieve compatibility associated with the bit assignment of CGMS-A, when “XX0000” is written in the first 6 bits, a word of 8 bits immediately after the first 6 bits is used to describe CGMS-A.
In the case where the 20th and 283rd lines are used to describe CGMS-A, when a video signal is produced and distributed according to the Japanese CPR-1204 standard, an aspect ration is described in the first 2 bits of the identification signal, and the first 2 bits of the identification signal are regarded, by a video playback apparatus designed and produced according to the CPR-1204 standard, as representing the aspect ratio. On the other hand, in the case where a video signal is produced and distributed according to the EIA-805 standard of the USA, information other than the aspect ratio is described in the first 2 bits of the identification signal, and video playback apparatuses designed and produced according to the EIA-8085 standard regard the first 2 bits of the identification signal as representing information other than the aspect ration. Note that the term “video playback apparatus” is used to describe a wide variety of apparatuses such as a BS digital set top box (STB), a DVD player, a video recorder, and the like.
When a video playback apparatus produced in Japan according to the CPR-1204 standard is exported to the USA and it is used to play back a video content produced or distributed in the USA, the video playback apparatus produced in Japan will treat, as the aspect ratio information, the first 2 bits of an identification signal indicating information other than the aspect ratio. As a result, an erroneous operation occurs. Conversely, when a video playback apparatus produced in the USA according to the EIA-805 standard is imported to Japan and it is used to play back a video content produced or distributed in Japan, the video playback apparatus produced in the USA will regard the aspect ration information as information other that the aspect ratio, and thus an erroneous operation occurs.